Apparatus for producing ammonia

ABSTRACT

The invention relates to a device for generating ammonia from an ammonia precursor solution, having a reaction space with an inflow connector through which an exhaust-gas flow can flow into the reaction space, having an outflow connector through which an ammonia-containing gas flow can exit the reaction space, and having a supply device by way of which selectively an ammonia precursor solution or a fuel can be supplied into the reaction space.

The invention relates to a device for generating ammonia from an ammoniaprecursor solution. A device of said type may for example be used forgenerating ammonia that is utilized for exhaust-gas purification in anexhaust-gas treatment device. Exhaust-gas treatment devices in whichammonia is utilized for exhaust-gas purification are for examplecommonly used for the purification of exhaust gases of diesel internalcombustion engines in motor vehicles. Nitrogen oxide compounds in theexhaust gas of the internal combustion engine are reduced with the aidof the ammonia. As ammonia precursor solution, use is typically made ofurea-water solution. An ammonia precursor solution of said type has theadvantage over ammonia that it can be stored in a tank without problems.What is particularly commonly used is a urea-water solution with a ureacontent of 32.5%, which is available under the trade name AdBlue®.

The conversion of ammonia precursor solution into ammonia generallynecessitates special technical measures Ammonia is obtained from theammonia precursor solution for example at certain temperatures. Theconversion takes place in a particularly effective manner in atemperature range between 200° C. and 550° C.

The temperature range for the conversion of ammonia precursor solutioninto ammonia may be expanded, and in particular lowered, by the presenceof catalytic converters, such that the conversion can even take place ina temperature range between 140° C. and 250° C. The thermal conversionof ammonia precursor solution into ammonia is normally referred to asthermolysis or as thermolytic conversion. If the conversion isadditionally assisted by way of a catalytic converter, this is referredto as hydrolysis or hydrolytic conversion.

In any case, the ammonia precursor solution must be heated in order tobe converted into ammonia. Heat energy is required for this purpose.Normally, the ammonia precursor solution is thus metered directly intothe exhaust gases of an internal combustion engine. The heating is thenrealized by way of the exhaust gases. Here, there is however the problemthat, in particular in the case of diesel internal combustion engines,the exhaust gases are commonly at relatively low temperatures andtherefore (at least in many load states of the diesel engine, inparticular also at idle) cannot provide enough thermal energy to convertammonia precursor solution into ammonia in an effective manner Wherepossible, it has then been the approach to avoid dosing of ammonia insaid time periods. If this was not possible, this problem has generally,in the past, been counteracted with the aid of suitable measures forincreasing the temperature in an exhaust-gas treatment device. Theheating of the exhaust gases is particularly commonly performed with theaid of an electric heater. A further known method for increasing thetemperature of the exhaust gases is the intentional shifting of theoperating point of the internal combustion engine such that the internalcombustion engine generates exhaust gases at relatively hightemperature. Here, there is however the problem that, in particular ifammonia precursor solution is not fully converted into ammonia, depositsof the ammonia precursor solution can form in the exhaust-gas treatmentdevice. Such deposits can (permanently) adversely affect the exhaust gaspurification, impair the efficiency and consumption, and/or even damagethe exhaust-gas treatment device. Furthermore, a situation may arise inwhich the exhaust gas temperature is too low to be able, by way of thedescribed known measures for increasing the temperature, to adequatelyincrease the exhaust-gas temperature for the conversion of ammoniaprecursor solution into ammonia. This applies in particular tocold-start phases of an internal combustion engine because, incold-start phases, the exhaust gases of the internal combustion engineare intensely cooled by the thermal mass of the internal combustionengine and of the exhaust-gas treatment device.

It is an object of the present invention to specify a device forgenerating ammonia from an ammonia precursor solution, which device isimproved in relation to the prior art and is in particular capable ofproviding ammonia substantially independently of the temperaturesprevailing in an exhaust-gas treatment device.

Said objects are achieved by means of a device according to the featuresof claim 1. Further advantageous embodiments of the invention arespecified in the dependent claims. The features specified individuallyin the claims may be combined with one another in any desiredtechnologically meaningful way and may be supplemented by explanatoryfacts from the description, with further embodiments of the inventionbeing highlighted.

The invention relates to a device for generating ammonia from an ammoniaprecursor solution, having a reaction space with an inflow connectorthrough which an exhaust-gas flow can flow into the reaction space,having an outflow connector through which an ammonia-containing gas flowcan exit the reaction space, and having a supply device by way of whichselectively an ammonia precursor solution or a fuel can be supplied intothe reaction space.

The devices designed in particular as a component which is positionedexternally or adjacent to an exhaust line with the main exhaust-gas flowof an internal combustion engine. The device is typically connected to aline branch which branches off from an exhaust line of an exhaust-gastreatment device of an internal combustion engine. Said line branch thenopens into the inflow connector of the device. The line branchpreferably branches from the exhaust-gas treatment device upstream of anexhaust gas turbocharger which is integrated in the exhaust line. Asupply line is typically connected to the outflow connector of thedevice, via which supply line the ammonia-containing gas flow generatedby the device is supplied to the exhaust-gas treatment device. Thesupply line opens, preferably downstream of the turbocharger in theexhaust-gas flow direction, into the exhaust-gas treatment device of theinternal combustion engine. The device is thus particularly preferablyintegrated in an exhaust-gas bypass which bypasses the turbocharger.This has the advantage that a pressure difference prevails between theinflow connector and the outflow connector, which pressure differenceensures that the exhaust gases that are conducted into the inflowconnector are forced through the device with a pressure gradient.

The reaction space refers to a (at least one) cavity within the device,in which cavity the conversion reaction of ammonia precursor solutioninto ammonia takes place. The reaction space may comprise a component orvarious functional components which promote the conversion reaction.These are for example (a) special catalytic converters, (b) structureswhich influence the exhaust-gas flow and the movement of the ammonia andof the ammonia precursor solution in the reaction space, and/or (c)sensors etc.

The supply device preferably comprises at least one nozzle by way ofwhich the ammonia precursor solution and/or a fuel can be metered intothe reaction space. The supply device preferably furthermore comprisesat least one valve by way of which the supply of ammonia precursorsolution and/or of fuel can be (actively) controlled. The valve has thetask in particular of controlling the amount of ammonia precursorsolution supplied and the amount of fuel supplied. This may be realizedfor example by way of an adaptation of the opening time of the at leastone valve. Here, the duration of the opening time is proportional to thesupplied amount of ammonia precursor solution and/or proportional to thesupplied amount of fuel.

The supply device of the device described here has the property thatboth ammonia precursor solution and fuel can be supplied by way of saidsupply device. This means that, by way of the supply device, ammoniaprecursor solution and fuel can be supplied to the reaction space inparallel and/or with a time offset with respect to one another.

The ammonia precursor solution has already been described in detailfurther above. A “fuel” refers in particular to a hydrocarbon-containingfluid (liquid and/or gas) which can be burned together with oxygen andwhich thus contributes to an intense temperature increase. Fuels are forexample the fuels that are commonly used in motor vehicles, such as forexample gasoline or diesel. Diesel fuel is particularly preferably usedas fuel for the device, because diesel fuel is available in any case inmotor vehicles with a diesel internal combustion engine (for which thedevice described here is particularly suitable).

By way of the supply device of the device being discussed here, whichsupply device performs both the supply of ammonia precursor solution andthe supply of fuel, it is possible for fuel to be supplied to thedevice. Fuel can be burned in the device such that the temperature inthe device is increased and lies in the temperature range required forthe conversion of ammonia precursor solution into ammonia. The increaseof the temperature with the aid of fuel is particularly efficientbecause suitable fuel (for example diesel fuel) is generally availablein any case in motor vehicles. The temperature increase is realized inparticular by virtue of the fuel being dispensed onto a catalyticallyactive surface, where the fuel ignites.

Furthermore, the temperature increase may also be achieved by virtue ofthe fuel being ignited by way of a flame or a spark. The temperatureincrease with the aid of fuel can in particular be considerably fasterthan the temperature increase with the aid of an electric heater.Specifically, in a motor vehicle, it is generally the case that there isonly a limited availability of electrical energy, because electricalenergy must be generated in a cumbersome manner by way of a generator.

Furthermore, the described device has the great advantage that only asmall (branched-off) part of the exhaust gases of an internal combustionengine flows through the device, and must be heated in the device, ifthe exhaust-gas temperature lies below the temperature required for thereaction of ammonia precursor solution into ammonia. The heating of theexhaust gases in the device can thus be performed with considerablyreduced energy consumption than in devices which (only) permit heatingof the entire exhaust-gas flow of an internal combustion engine.

The device is particularly advantageous if the supply device comprises adosing valve which has a first feed line for ammonia precursor solutionand a second feed line for a fuel.

It is then possible for a feed-in line for ammonia precursor solution tobe connected to the first feed line and for a feed-in line for fuel tobe connected to the second feed line. In the supply device there ispreferably provided at least one valve by way of which the amount offuel and the amount of ammonia precursor solution supplied to the devicecan each be precisely set (preferably separately from one another). Thesupply device particularly preferably comprises a multi-way valve by wayof which selectively ammonia precursor solution or fuel can be supplied.The supply device preferably has a common nozzle by way of which bothfuel and ammonia precursor solution can be metered. It is then the casethat selectively ammonia precursor solution or fuel passes through thenozzle into the reaction space of the device. The supply of fuel resultsin a temperature increase in the device. When the device has heated upto a sufficient extent, ammonia precursor solution is supplied. Theammonia precursor solution is converted into ammonia in a particularlyeffective manner in the heated device. If the temperature of the devicefalls again, the supply of ammonia precursor solution can be ended againand fuel can be supplied to the device or to the reaction space of thedevice again, such that the temperature is increased again to thetemperature required for the generation of ammonia, and metering ofammonia precursor solution can be performed again.

The device is particularly advantageous if, in the reaction space, thereis arranged an impingement structure toward which the supply device isoriented and which is impinged on by the supplied ammonia precursorsolution.

An impingement structure of said type may for example be in the form ofa honeycomb body through which the exhaust-gas flow can flow, the facesurface of which honeycomb body is impinged on by the ammonia precursorsolution and/or by the fuel. An impingement structure of said type is inparticular arranged within the device such that it is heated in aneffective manner by the fuel and/or by the exhaust gases entering thedevice. The impingement structure is preferably not in direct contactwith an outer wall of the device. The outer wall of the device ispossibly cool because it is in contact with the surroundings. Theimpingement structure is preferably arranged in cantilevered or at leastpartially cantilevered form in the reaction space. The impingementstructure is preferably arranged so as to at least partially span thecross section of the reaction space.

The device is furthermore advantageous if the impingement structure isprovided with a coating which catalyzes both a hydrolysis of ammoniaprecursor solution into ammonia and an exothermic reaction of fuel withoxygen.

A coating of said type comprises, for example, one of the followingcomponents of catalytically active material: a) titanium dioxide,aluminum dioxide and gold; b) titanium dioxide, platinum and palladium.

A catalytically active coating which promotes an exothermic reaction ofthe fuel with oxygen is particularly advantageous because a coating ofsaid type reduces the ignition temperature of the fuel, and it is thuspossible in particular for local temperature peaks in the device to beprevented. If appropriate, it is also possible by way of a catalyticallyactive coating to avoid the need for an open flame for the conversion ofthe fuel in the device. Also, in this way, the thermal loads within thedevice can be kept low. Furthermore, it is possible for no separateand/or electrical ignition to be required for the initiation of thecombustion, with the conversion of the fuel rather startingspontaneously upon the supply of the fuel into the reaction space of thedevice. The oxygen required for the combustion of the fuel normallyenters the reaction space with the exhaust gas through the inflowconnector. In particular in the case of lean-burn diesel internalcombustion engines, a high oxygen fraction is normally encountered inthe exhaust gas. As an alternative or in addition to the oxygen, it isalso possible for incompletely oxidized exhaust-gas constituents, suchas carbon monoxide or nitrogen monoxide, to be converted with the fuel.

The device is furthermore advantageous if the supply device comprises acommon nozzle by way of which ammonia precursor solution and fuel aresprayed into the reaction space, wherein the nozzle generates differentspray patterns with ammonia precursor solution and with fuel.

Here, the expression “common” nozzle means that both the ammoniaprecursor solution and the fuel pass into the reaction space through thesame nozzle. A spray pattern refers here in particular to the shape of aspray cone that is formed when ammonia precursor solution and/or fuelemerge(s) through an outlet opening of the nozzle. The fuel that is usedand the ammonia precursor solution may have different flowcharacteristics. In particular with regard to the viscosity, thedensity, the temperature capacity and/or the surface tension, the fuelthat is used and the ammonia precursor solution generally differgreatly. It is therefore possible for a nozzle for the supply of ammoniaprecursor solution and fuel to be designed such that the spray patterngenerated by the nozzle with fuel and the spray pattern generated by thenozzle with ammonia precursor solution differ from one another (e.g.with regard to the spray direction, the spray cone angle, the spraydroplet size, etc.).

Furthermore, it is also possible for ammonia precursor solution and fuelto be provided at the nozzle with different pressures. The pressureprevailing at the nozzle also influences the spray pattern at thenozzle. For example, the ammonia precursor solution may be provided atthe nozzle with a pressure of up to 8 bar, whereas the fuel is providedat the nozzle with a significantly different pressure, for example(depending on the specific pump-nozzle system and a desired spray form)with a relatively low pressure (e.g. lower than 5 bar) and/or with arelatively high pressure (e.g. at least 20 bar, at least 50 bar or evenmore than 200 bar). Then, the fuel is generally atomized very much morefinely than the ammonia precursor solution. Normally, it is in the casethat a more widely angled spray cone forms for the fuel than for theammonia precursor solution. Furthermore, it is then also possible forthe formation of different spray cones to be promoted by way of theconstruction of the nozzle. This may be realized for example by way ofsuitable diversions of the ammonia precursor solution and/or of the fuelin the nozzle. Such diversions have a different effect on the differentliquids (fuel and ammonia precursor solution), such that this promotesdifferent spray patterns.

It is possible for a carrier gas, in particular compressed air, to beused for the metering of ammonia precursor solution and/or fuel. It isalso possible in this way for the predefined pressure during themetering of the ammonia precursor solution and/or of the fuel to beinfluenced or adapted.

The device is furthermore advantageous if different impingement regionsfor ammonia precursor solution and for fuel are provided within thereaction space.

Such different impingement regions may be realized for example by way ofa correspondingly targeted configuration of the different spray patternsfor ammonia precursor solution and for fuel. It is particularlypreferable if, for ammonia precursor solution, as a spray pattern, acentral conical spray cone is generated which impinges centrally on animpingement structure in the device and, for fuel, a widened spray coneis generated in the case in which no fuel is sprayed in a centralregion, resulting in a ring-shaped impingement region for fuel on theimpingement structure, wherein the ring-shaped impingement region forfuel is arranged around a central impingement region for ammoniaprecursor solution.

With such a configuration of the different impingement regions forammonia precursor solution and for fuel, it is possible for in each casetargetedly suitable different coatings to be provided on the impingementstructure in the different impingement regions, wherein a firstcatalytically active coating which promotes the catalytic conversion ofammonia precursor solution into ammonia is provided in the firstimpingement region in which ammonia precursor solution impinges on theimpingement structure, whereas a second catalytically active coatingwhich promotes the conversion reaction of fuel for heat generationpurposes is provided in the second impingement region.

The device is furthermore advantageous if an electric heater is arrangedin the reaction space.

By way of an electric heater, the device can be heated in a particularlyeffective manner In particular, it is possible for the device to beheated even in the presence of particularly low temperatures at whichthe generation of heat with the aid of fuel would not be possible atall, for example because a minimum temperature for the catalyticconversion of the fuel with oxygen has not yet been reached.

It is particularly advantageous if the electric heater simultaneouslyforms the impingement structure within the device. The increasedtemperature within the device is required in particular in the region ofthe impingement structure because it is there that cooling by way of theimpinging ammonia precursor solution occurs. Furthermore, an increasedtemperature is required specifically on the impingement structure inorder to effect the conversion reaction of the ammonia precursorsolution. The electric heater contributes to the capability ofmaintaining a minimum temperature and/or a heat range for the dosing.Furthermore, owing to the contact with the ammonia precursor solution,this promotes faster heat transport into the droplets. At the same time,a high level of turbulence can be generated, such that, for example,so-called “Leidenfrost effects” can be substantially or even entirelyeliminated. Furthermore, it is thus also possible for an adequately highheat capacity to be provided in order that the impinging dropletsthemselves do not effect significant cooling of the electricheater/impingement structure, and thus the conversion reaction can takeplace in an effective manner uniformly and/or quickly.

The device is particularly advantageous if the electric heater is anelectrically heatable honeycomb body.

An electrically heatable honeycomb body is suitable in particular forforming, with the aid of an electric heater, an impingement structurewhich can at the same time be flowed through by the exhaust-gas flow. Anelectric honeycomb body may for example be a heating coil formed frommetallic foils, which heating coil spans the cross section of the deviceor a cross section of the reaction space of the device.

Furthermore, the device is advantageous if the inflow connector isarranged tangentially at the reaction space.

By way of a tangential arrangement of the inflow connector, it can beensured that the exhaust gas flowing into the inflow connector generatesa vortex flow within the device. Said vortex flow firstly has theadvantage that particularly good mixing of ammonia precursor solution,fuel and exhaust gas takes place. Furthermore, the vortex flow centersthe fuel and/or the ammonia precursor solution within the device andensures that the fuel and/or the ammonia precursor solution does notcome into contact, or comes into contact only to a small extent, with anouter wall of the device. It is thus possible for the formation ofdeposits of the fuel and/or of the ammonia precursor solution on theouter wall of the device to be prevented.

Furthermore, the device is advantageous if the reaction space is dividedby a cylindrical diverting element into a cylindrical gap and a centralchamber, wherein the cylindrical gap and the central chamber areconnected to one another by way of a diverting region, wherein theinflow connector is arranged at the cylindrical gap, the exhaust-gasflow from the cylindrical gap is conducted into the central chamberthrough the diverting region, and the supply device supplies theprecursor solution and the fuel in an axial direction into the centralchamber through the diverting region.

The entire device preferably has a cylindrical housing. Here, the supplydevice is arranged on a face surface of the cylindrical housing, whereinthe supply device is oriented in an axial direction toward saidcylindrical housing. The outflow connector is preferably arranged on theopposite face side of the cylindrical housing. The inflow connectoropens into the cylindrical housing through a circumferential surface ina tangential direction. The reaction space is arranged within thecylindrical housing of the device. The diverting element is thenarranged in the direction toward the outflow connector proceeding fromthe supply device, which diverting element separates the cylindrical(ring-shaped) gap from the central chamber of the reaction space. Thecylindrical gap is preferably open only in the direction of the supplydevice, and closed off on the opposite side. The exhaust gas that entersthrough the inflow connector therefore passes from the cylindrical gapinto the central chamber in a diverting region in the vicinity of thesupply device. In the diverting region there is preferably also aperforated screen, wherein the exhaust-gas flow passes through saidperforated screen on the path from the cylindrical gap into the centralchamber. Said perforated screen preferably has a large central openingthrough which the metering device meters the fuel and/or the ammoniaprecursor solution into the central chamber. The spray cone of thesupply device, as described further above, preferably extends throughsaid central opening. It is preferable for a multiplicity of smallopenings to be arranged around the central opening, which small openingspromote the entry of the exhaust gas into the central chamber. Theimpingement structure already described is arranged in an axialdirection and in the direction of the outflow connector proceeding fromthe supply device (downstream of the diverting element), whichimpingement structure spans the cross section of the device and of thereaction space and may also comprise an electric heater. Additionalcatalytic converter substrate bodies may be situated so as to follow theimpingement structure in an axial direction, which additional catalyticconverter substrate bodies contribute to the conversion of the ammoniaprecursor solution into ammonia. Sensors and further components by wayof which the generation of ammonia in the device can be assisted and/ormonitored may also be arranged there. A sensor of the device maycomprise in particular a temperature sensor and/or a lambda probe by wayof which an oxygen fraction in the gas can be determined.

The externally arranged cylindrical diverting element has the advantagethat thermal insulation of the central chamber with respect to the outerwall of the device is realized, such that the ammonia precursor solutionthat is supplied into the central chamber cannot come into contact withthe outer wall of the device. Furthermore, by way of the cylindricaldiverting element, heating of the central chamber is realized, becausethe exhaust gas flowing in through the inflow connector flows around andheats the central chamber (through the cylindrical gap) before saidexhaust gas enters the central chamber through the diverting region.

Also proposed is an exhaust-gas treatment device for the purification ofthe exhaust gases of an internal combustion engine, having a device forgenerating ammonia as described here, wherein the inflow opening isconnected by way of a line branch to an exhaust line of the exhaust-gastreatment device, and the outflow opening is connected by way of asupply line to the exhaust line, wherein, through the inflow opening,between 0.1% and 5.0% of the exhaust gas from the internal combustionengine flows into the reaction space.

As already described, the line branch branches off from the exhaust linepreferably upstream of the turbocharger, whereas the supply line opensinto the exhaust line downstream of the turbocharger. For this reason,it is advantageous for only a relatively small exhaust-gas flow to bebranched off from the main exhaust line and to flow into the devicethrough the inflow connector. The main exhaust-gas flow can then be usedin the turbocharger to generate mechanical energy for the superchargingof the internal combustion engine. Furthermore, such a small exhaust-gaspartial flow of between 0.1% and 5% of the exhaust gas can be heated ina particularly effective manner with the aid of the fuel and/or with theaid of an electric heater, because relatively little thermal energy isrequired for this purpose.

An SCR catalytic converter on which nitrogen oxide compounds in theexhaust gas can be reduced with the aid of the generated ammonia to formnon-harmful substances is preferably arranged in the exhaust gastreatment device.

An exhaust-gas treatment device of said type is particularly preferablyused for the purification of the exhaust gases of a diesel internalcombustion engine. The exhaust-gas treatment device and the device arein particular also suitable for exhaust-gas purification in watercraft,rail vehicles, agricultural machines and construction machines etc. Thedevice and the exhaust-gas treatment devices are particularly suitablein applications in which the exhaust gases of an internal combustionengine which is operated predominantly in the part-load range and in thelow-load range are purified, because low exhaust-gas temperatures areparticularly commonly encountered then.

The invention and the technical field will be explained in more detailbelow on the basis of the figures. The figures show particularlypreferred exemplary embodiments, to which the invention is however notrestricted. It is pointed out in particular that the figures, and inparticular the dimensional relationships illustrated in the figures, aremerely schematic. In the figures:

FIG. 1: shows a described device,

FIG. 2: shows a cross section through a first embodiment of a describeddevice,

FIG. 3: shows a cross section through a second embodiment of a describeddevice, and

FIG. 4: shows a motor vehicle having a described device.

FIG. 1 illustrates a device 1 which has a cylindrical housing 38.Situated on one face side of the cylindrical housing 38 of the device isthe supply device 5 by way of which fuel (e.g. diesel fuel) and/orammonia precursor solution (e.g. urea-water solution) can be supplied tothe device. For this purpose, the supply device 5 has a first feed line7 for the metering of ammonia precursor solution and a second feed line8 for the metering of fuel. The supply device 5 also comprises a dosingvalve 6 by way of which the fuel and the ammonia precursor solution canbe (selectively) dosed. The supply device 5 supplies the fuel and/or theammonia precursor solution into a reaction space 2 of the device 1 in anaxial direction 22. Here, the fuel and/or the ammonia precursor solutionis sprayed with a spray pattern 11.

The outflow connector 4 is arranged on the device 1 so as to be situatedopposite the supply device 5, through which outflow connector anammonia-containing gas flow can emerge from the device 1. The inflowconnector 3 is arranged on the circumferential surface of the device 1,via which inflow connector and exhaust-gas flow can enter the device.The reaction space 2 of the device 1 is divided by a diverting element18 into a cylindrical gap 19 and a central chamber 20. The cylindricalgap 19 and the central chamber 20 are connected to one another by way ofa diverting region 21 in the region of the supply device 5. In thediverting region 21 there is also provided a perforated screen 36 whichhas a central opening through which the supply device 5 can supplyammonia precursor solution and/or fuel into the central chamber 20 ofthe reaction space 2. The perforated screen 36 furthermore hasadditional, relatively small openings (arranged around the centralopening) through which the exhaust-gas flow can pass into the centralchamber 20.

The inflow connector 3 is preferably arranged tangentially at the device1. In this way, a vortex flow 28 is generated within the reaction space2 or within the cylindrical gap 19 and the central chamber 20.

Within the device 1, an impingement structure 9 is arranged downstreamof the diverting element 18 and the central chamber 20 as viewed in theexhaust-gas flow direction, which impingement structure forms a firstimpingement region 14 and a second impingement region 15, wherein thefirst impingement region 14 is provided for receiving ammonia precursorsolution and the second impingement region 15 is provided for receivingfuel. In the present embodiment of a device 1, the impingement structure9 is in the form of an electric heater 16, and particularly preferablyin the form of an electrically heatable honeycomb body 17. Arrangeddownstream of the impingement structure 9 in the flow direction is atleast one catalytic converter substrate body 32 which may comprisecoatings for the chemical conversion of the ammonia precursor solutionand/or of the fuel. Furthermore, a sensor 33 is also provided in thedevice 1, by way of which sensor the conversion of ammonia precursorsolution into ammonia in the device 1 can be monitored. The sensor 33may for example comprise a temperature sensor and/or a lambda probe byway of which an oxygen content in the gas can be determined.

FIGS. 2 and 3 each show sections through different embodiments of thedevice 1 from FIG. 1 in a section direction arranged perpendicular tothe axial direction. It is possible in each case to see the tangentiallyarranged inflow connector 3 and the diverting element 18, the housing38, the cylindrical 19 and the central chamber 20. It is also possibleto see the first impingement region 14 and the second impingement region15. In FIG. 2, the second impingement region 15 is arrangedconcentrically around the first impingement region 14. In FIG. 3, analternative embodiment has been selected in which the first impingementregion 14 and the second impingement region 15 in each case formquarters of a circular basic area. Such a division between the firstimpingement region 14 for ammonia precursor solution and the secondimpingement region 15 for fuel can be realized by way of a suitableembodiment of the supply device and in particular of the nozzle of thesupply device. In the first impingement region 14 there is provided afirst coating 12 which serves for the conversion of the ammoniaprecursor solution into ammonia. In the second impingement region 15there is provided a second coating 13 which serves for the thermalconversion of the fuel.

FIG. 4 shows a motor vehicle 24 having an internal combustion engine 27and having an exhaust-gas treatment device 23 for the purification ofthe exhaust gases of the internal combustion engine 27, whichexhaust-gas treatment device is connected to the internal combustionengine 27 by way of an exhaust line 26. The internal combustion engine27 furthermore has an intake line 34 via which the internal combustionengine 27 draws in air (from the surroundings). The motor vehicle 24also has a turbocharger 29 by way of which the intake air of theinternal combustion engine 27 can be supercharged or compressed. Theturbocharger 29 is driven by the exhaust gases flowing through theexhaust line 26. A line branch 25 branches off from the exhaust line 26upstream of the turbocharger 29, which line branch leads to a describeddevice 1. The ammonia generated by the device 1 is supplied into theexhaust line 26, downstream of the turbocharger 29 as viewed in theexhaust-gas flow direction, via a supply line 35, such that the ammoniathat is generated can be used in the exhaust-gas treatment device 23 forthe purposes of exhaust-gas purification. An SCR catalytic converter 37is arranged in the exhaust-gas treatment device 23, by way of which SCRcatalytic converter nitrogen oxide compounds in the exhaust gas of theinternal combustion engine 27 can be converted together with the ammoniafrom the device 1. The device 1 is supplied with fuel from a fuel tank31 and with ammonia precursor solution from a precursor solution tank30.

By way of the described device, the particularly reliable provision ofammonia for an exhaust-gas aftertreatment device is ensured even in thepresence of particularly low exhaust-gas temperatures. At the same time,a particularly small amount of energy is required for this purpose, andammonia can be provided in the form of an ammonia precursor solution andconverted into ammonia by the device. The device is suitable inparticular for the purification of diesel exhaust gases of internalcombustion engines which are often operated in the part-load range.

LIST OF REFERENCE SYMBOLS

1 Device

2 Reaction space

3 Inflow connector

4 Outflow connector

5 Metering device

6 Dosing valve

7 First feed line

8 Second feed line

9 Impingement structure

10 Nozzle

11 Spray pattern

12 First coating

13 Second coating

14 First impingement region

15 Second impingement region

16 Electric heater

17 Heatable honeycomb body

18 Diverting element

19 Cylindrical gap

20 Central chamber

21 Diverting region

22 Axial direction

23 Exhaust-gas treatment device

24 Motor vehicle

25 Line branch

26 Exhaust line

27 Internal combustion engine

28 Vortex flow

29 Turbocharger

30 Precursor solution tank

31 Fuel tank

32 Catalytic converter substrate body

33 Sensor

34 Intake line

35 Supply line

36 Perforated screen

37 SCR catalytic converter

38 Housing

1. A device for generating ammonia from an ammonia precursor solution,comprising: a reaction space with an inflow connector through which anexhaust-gas flow can flow into the reaction space, an outflow connectorthrough which an ammonia-containing gas flow can exit the reactionspace, and a supply device configured to selectively supply an ammoniaprecursor solution or a fuel into the reaction space.
 2. The device asclaimed in claim 1, wherein the supply device comprises a dosing valvewhich includes a first feed line for ammonia precursor solution and asecond feed line for a fuel.
 3. The device as claimed in claim 1,wherein, in the reaction space, there is arranged an impingementstructure toward which the supply device is oriented and which isimpinged on by the supplied ammonia precursor solution.
 4. The device asclaimed in claim 3, wherein the impingement structure is provided with acoating which catalyzes both a hydrolysis of ammonia precursor solutioninto ammonia and an exothermic reaction of fuel with oxygen.
 5. Thedevice as claimed in claim 1, wherein the supply device comprises acommon nozzle configured to spray ammonia precursor solution and fuelinto the reaction space, wherein the nozzle generates different spraypatterns with ammonia precursor solution and with fuel.
 6. The device asclaimed in claim 1, wherein different impingement regions for ammoniaprecursor solution and for fuel are provided within the reaction space.7. The device as claimed in claim 1, wherein an electric heater isarranged in the reaction space.
 8. The device as claimed in claim 7,wherein the electric heater comprises an electrically heatable honeycombbody.
 9. The device as claimed in claim 1, wherein the inflow connectoris arranged tangentially at the reaction space.
 10. The device asclaimed in claim 1, wherein the reaction space is divided by acylindrical diverting element into a cylindrical gap and a centralchamber, wherein the cylindrical gap and the central chamber areconnected to one another by a diverting region, wherein the inflowconnector is arranged at the cylindrical gap, the exhaust-gas flow fromthe cylindrical gap is conducted into the central chamber through thediverting region, and the supply device supplies the precursor solutionand the fuel in an axial direction into the central chamber through thediverting region.
 11. An exhaust-gas treatment device for thepurification of the exhaust gases of an internal combustion engine,comprising: a device for generating ammonia as claimed in claim 1,wherein the inflow connector is connected by a line branch to an exhaustline of the exhaust-gas treatment device, and the outflow connector isconnected by a supply line to the exhaust line, wherein, through theinflow connector, between 0.1 percent and 5 percent of the exhaust gasfrom the internal combustion engine flows into the reaction space.